Here science explains why in some cases they’ve reduced that calculated weight of certain dinosaurs approximately 50%. The depictions of these creatures in this piece of ancient art appears to provide some support for the idea of more muscular creatures than is often depicted(or not, judge for yourself). A problem that science seems to be trying to solves is; how under the current gravity could the larger dinosaurs run or even raise their necks?

Creationists and catastrophists might postulate a lower gravity in the past but this is not an acceptable answer for science who have built their house on uniformism…..s8int.com

Times Online
Jonathan Leake, Science Editor

WAS IT really the age of the thinosaurs? Scientists have discovered that dinosaurs may have been much lighter and sleeker than previously thought because of potential flaws in the equations used to calculate their weight.

The findings could force researchers to rethink many of their beliefs, particularly about giant plant eaters such as apatosaurus which had been thought to weigh up to 37 tons. The creatureâ€™s real weight was closer to 18 tons, according to new calculations.

Tyrannosaurus rex, the best-known predatory species, may have been far more lithe than imagined and able to move and turn at high speed.

â€śPalaeontologists have for 25 years used a statistical model to estimate the body weight of giant dinosaurs and other extraordinarily large extinct animals,â€ť said Gary Packard, from Colorado State University, whose research will appear in the Zoological Society of Londonâ€™s Journal of Zoology this week.

â€śWe have found that the statistical model is seriously flawed and the giant dinosaurs probably were only about half as heavy as is generally believed.â€ť

The research does not suggest that dinosaurs were shorter in length or height. These dimensions are clear from the size of their bones. Instead, Packardâ€™s work challenges the depiction of many giant herbivores. Until now they have been shown as well-rounded, powerful animals, when they are more likely to have been skinny and muscular.

Such findings would affect more than just appearance. It would suggest that these animals were leaner and faster, needed less food and had significant differences in lifestyle from what was previously thought.

Estimating the weight of dinosaurs has always been a problem for scientists, who have adopted two main approaches.

One involves measuring the remains of contemporary animal species and using them to build up a picture of how the dimensions of certain bones relate to the mass of a living body. The data can then be extrapolated for dinosaurs.

The other approach involves building models, either physically or on a computer, and using them to work out the volume that would be occupied by the body of a much larger creature of the same shape.

However, dinosaurs, especially giant herbivores such as the apatosaurus and diplodocus, have such different body plans from modern animals that errors creep in.

One problem is that such animals had light, strong spines but thick, powerful legs. Another problem is that they were simply much bigger than anything alive today. This means errors generated by using data from modern species become magnified when applied to large extinct ones.

John Hutchinson, a researcher in evolutionary biomechanics at the Royal Veterinary College in London, has tried to work out how much the tyrannosaurus might have weighed as part of his research into dinosaur locomotion.

â€śThe best we can do is put the weight at six to eight tons for a typical adult. There is a big question about how much skin they had and how much flesh. â€ť Hutchinson said.